Many threshold detecting devices are available today. Typically, threshold detection functions have been accomplished through the use of a differential comparator circuit. Such threshold detecting circuits are limited in their capabilities which correspondingly restricts their usage.
One desirable feature of a threshold detection circuit is the independence of the voltage threshold level with respect to ambient temperature. Most integrated electronic devices are designed to operate within a well defined operational temperature range.
To comply with the temperature independence requirement, more complicated circuits may be included in addition to the differential comparator circuit. With the added circuits to satisfy the above requirements, the threshold detection circuit becomes needlessly complex and cumbersome.
Another desirable feature of a threshold detection circuit is the ability to detect a threshold voltage substantially above the operating supply voltage.
In applications where the desired threshold voltage is substantially larger than the supply voltage, an auxiliary circuit, such as a resistor network, is typically required to step down the input voltage to a level below the supply voltage. This additional circuitry increases the size of the threshold detection circuit.
Accordingly, a need has arisen for a threshold detection circuit which has relatively few components, can maintain a substantially constant voltage threshold over a wide temperature range, and can detect a threshold voltage in excess of the supply voltage.